Why do I have to fast before taking some tests?


Fasting before certain blood tests is important to help make sure that your test results are accurate. Not all tests require fasting, but some do because the result is affected by food and drink. 

How will I know if the test I'm taking requires me to fast?

If you need to fast before taking your test, you'll be advised of this:

  • Before you buy your test- On the product page for the test.
  • When your purchase is confirmed - In the email you'll receive after you buy the test.
  • When you're ready to take/register the test - During the online registration process.

What are the rules of fasting? 

  • Stay hydrated by drinking clear water only (no squash or juices).
  • Try to take your sample in the morning.
  • Fast for at least 8 hours before taking your sample.
  • Discuss with your GP if fasting will affect your medication regime.
  • If you are feeling unwell because you are fasting, eat and take the test another day. 

What happens if I don't fast before collecting my sample?

If you don’t fast before taking a test that requires it, the reference ranges provided may not be accurate, and this may mean that you receive incorrect advice. If you forget to fast and you’ve eaten or drank something, or needed to eat because you felt unwell, please wait until the next day to take your test.